Relaxation in superconductors with large normal defects

Magnetic flux creep in a superconductor with large normal spherical defects is studied. The known coordinate dependence of the pinning energy allowed us to deduce the current dependence of the effective pinning barrier and the associated relaxation rate. A nonlinear differential equation governing the flux creep was derived. A macroscopic characteristic length determining the scale of the spatial flux changes was found. Magnetic flux density profiles during the penetration and relaxation processes were calculated for various mean defect size, R